Biological role and agronomic significance of carbohydrates in plant life activities

Carbohydrates are the most important element of plant vital activity, determining their strength, resistance to adverse factors, and energy balance. In practical agronomy, carbohydrate metabolism directly influences the resistance of crops to lodging, drought, and pathogens. The final yield and product quality depend on how efficiently the plant synthesizes and distributes sugars.

In living organisms, carbohydrates perform six key functions:

• energy;
• plastic;
• protective;
• structural;
• regulatory;
• storage.

The energy and plastic roles of carbohydrates are inextricably linked to crop growth. Oxidizing in the process of respiration, they release latent chemical energy and meet the majority of the organism's needs. As a plastic material, carbohydrates are necessary for the biosynthesis of organic and nucleic acids, from which proteins, amino acids, and lipids are subsequently built. They are also used for the synthesis of homo- and heteropolysaccharides — essential structural components of connective tissues (e.g., mucopolysaccharides).

Protective and structural properties of carbohydrates form a physical barrier against aggressive environmental factors. They participate in the construction of the external skeleton of insects and crustaceans, and form the basis of plant cell walls and cell membranes of all living organisms. It is the strong cellulose framework that provides stem resistance to lodging under wind load. In animals and humans, carbohydrates, in combination with proteins, are part of cartilage tissues (chondroitin sulfates), and in the liver, glucuronic acid binds toxins, converting them into soluble ethers for excretion with urine.

Regulation of water regime and accumulation of carbohydrates in tissues

In regulating plant vital activity, carbohydrates work as fast dispatchers. Mutual transformations of starch and sugars in the guard cells of stomata control their opening and closing, regulating transpiration. Monosaccharides actively participate in the regulation of osmotic processes, helping cells retain water during drought. At the cellular level, carbohydrate markers on membranes allow the organism to distinguish its own cells from foreign ones, and the sugars themselves are part of nucleic acids responsible for the transmission of hereditary information. In animals, they prevent the accumulation of ketone bodies during fat oxidation (if this process fails, for example in diabetes mellitus, acidosis develops), and fiber mechanically stimulates intestinal peristalsis.

The storage function allows plants to accumulate reserves in the form of starch, inulin, and fructosans. In the process of photosynthesis, primary starch is formed in chloroplasts, which is then converted into sugars for transport through tissues. In the leucoplasts of storage organs, these sugars turn back into secondary starch. For plants of the Asteraceae family, the main reserve substance is inulin, which replaces starch.

Inulin accumulates in underground organs and is contained in large quantities in the tubers of Jerusalem artichoke and dahlia, in the roots of dandelion, kok-saghyz, chicory, and artichoke, as well as in all parts of the rubber-bearing guayule (Parthenium argentatum). It is found in the cell sap as a colloidal solution and, when interacting with alcohol, precipitates into spherocrystals. In the process of inulin hydrolysis, fructose is formed according to the following reaction:

(С6Н10О5)n + nH2O = nC6H12O6

Animals and humans store carbohydrates in the form of glycogen, which accumulates primarily in the liver. In the body of a regularly fed animal, its content can reach 10% of the tissue mass. During starvation, this reserve is quickly consumed, and its concentration drops to 0.2%.